Intermicellar Distance Research Articles

Evidence for Sodium Dodecyl Sulfate/Protein Complexes Adopting a Necklace Structure

Structural analysis by cryo-electron microscopy and small-angle X-ray scattering of ten sodium dodecyl sulfate/protein complexes in 25 mM Tris/HCl, 0.192 M glycine, pH 8.3, showed necklace-like structures of spherical micelles dispersed along the unfolded peptide chain. The micelles of most SDS/protein complexes had a constant diameter (approximately 6.2 nm), slightly larger than pure SDS micelles (approximately 5.7 nm), all micelles possessing a degree of surface roughness. The micelle-associated polypeptide is mostly situated at the interface of the sulfate head groups and hydrocarbon core, intruding into the core rather than outward from the surface. Proteins with a molecular mass less than about 20 kDa formed complexes with a single SDS micelle. Multi-micellar SDS/protein complexes had centre-to-centre intermicellar distances in the range 7.0-12.0 nm. Our findings on the constancy of micellar size, number of micelles/complex, and the relationship between the degree of occupancy of micelles and a polypeptide's molecular mass, have enabled us to speculate on the correlation between the electrophoretic mobility of a polypeptide in SDS/PAGE and its molecular mass. The anomalous electrophoretic behaviour observed for the sodium dodecyl sulfate/histone H5 complex is accounted for by the large micelle of its complex.

The effect of micellar lifetime on the rate of solubilization and detergency in sodium dodecyl sulfate solutions

The slow relaxation time (τ2) of sodium dodecyl sulfate (SDS) micelles, measured by the pressure‐jump technique, was maximum at 200 mM concentration at 25°C, indicating that the most stable micelles are formed at this concentration. This is presumably related to the optimum molecular packing in the micelle. The rate of solubilization of benzene and Orange OT dye into SDS solutions was also maximum at 200 mM concentration. The results are explained as follows: The distance between micelles (i.e., intermicellar distance) decreases as the surfactant concentration (or the number of micelles) increases, resulting in a stronger electric repulsion between micelles. Therefore, the micelles become more rigid, due to the compressive force of intermicellar repulsion, as the concentration increases up to 200 mM SDS. With further increase in the SDS concentration, the micellar shape changes from spherical to cylindrical to accommodate more surfactant molecules in the solution and to minimize the free energy of the system. The interior of the tightly packed micelles is more hydrophobic than that of loosely packed micelles and, therefore, the tightly packed micelles induce rapid solubilization of nonpolar molecules (e.g., benzene, Orange OT) into these micelles.

PGSE-NMR & Sans from TPB Based Microemulsions

ABSTRACTSelf-diffusion coefficients from pulsed-gradient spin-echo NMR are reported for four components of the tetradecylpyridinium bromide - 85% heptane/15% pentanol - water pseudoternary system. Measurements were taken throughout the inverted microemulsion region and also in a small isotropic region beyond the domain of lamellar liquid crystals. Observations of the self-diffusion coefficients for water relative to those of the surfactant, oil and alchohol show several distinct structural transitions within the water-in-oil region of the phase diagram. The smaller isotropic region exhibits a complete inversion of phase relative to the water-in-oil region. Conductivity measurements were used to further clarify the NMR data. Subsequent small angle neutron scattering (SANS) measurements on the same system show the transition from the single particle (heavy water + Stern layer droplet) scattering regime at low water concentration to the mixed single/interdroplet scattering regime when the intermicellar distance becomes comparable to the size of the micelles.

Reactivity of functional amino acid residues in silk fibroin of philosamia cynthia ricini towards monoepoxides.

The heterogeneous addition reaction of the silk fibroin fibers of Philosamia cynthia ricini with various monoepoxides was investigated in ethanol and cyclohexane at 45-75°C after the fibers were padded with aqueous solutions of various salts as catalysts. The reactivity of the main functional amino acid residues was found to decrease in the order: histidine _??_ tyrosine _??_ arginine. The concentration of the aqueous salt solutions influenced the reactions of tyrosine and arginine, but did not affect largely those of histidine and lysine. The reaction rate of tyrosine was discussed in terms of the nucleophilicity of the anions of the catalyst. The reactions of tyrosine and histidine depended on both of the polar and steric factors of the substituents of the epoxides. Their effect was elucidated by the modified Taft equation. The reactivity difference of tyrosine, arginine, and histidine between Philosamia cynthia ricini and Bombyx mori silk fibroins towards the epoxide was partly explained with swellability and intermicellar distance of the fibroin fibers and the amino acid composition of the fibers.

“Ordered” Distribution of Ionic Micelles in Dilute Solutions of Alkyltrimethylammonium Chloride as Studied by Small‐Angle X‐ray Scattering

AbstractThe solutions of ionic micelles of dodecyl‐, tetradecyl‐ and hexadecyl‐trimethylammonium chlorides were studied by small‐angle X‐ray scattering (SAXS). The SAXS curves showed a single, broad peak. The interference functions S(Q) were obtained from the scattering curves. The radial distribution function g(r) was calculated from S(Q) and the distances between nearest neighboring micelles were evaluated. The intermicellar distances (rm) evaluated from g(r) were close to the average distance calculated by assuming a uniform distribution of the micelles throughout the solution. This fact indicates that the intermicelle attractive force through the intermediary of counterions was weak, because the number of charges on the micelles was small. A difference between rm and the Bragg spacing calculated from the overall intensity of scattered X‐ray was noticed but it was not large enough to invalidate our previous interpretation that the Bragg spacing is an approximate measure of the ordered structure. By taking into account the paracrystalline distortion, the lattice factor Z(Q) was calculated. Excellent agreement was obtained with the structure factor S(Q) for a face‐centered cubic lattice structure when the distortion factor was assumed to be about 0.2. The number of peaks of the lattice factor decreased with increasing distortion factor. This suggests the incorrectness of the often expressed view that the single broad peak is not reminiscent of some kind of ordering: in this view the large distortion, which exists in solutions and at ambient temperatures, has been overlooked.

Structural and Orientational Characteristics of the Disodium/Cromoglycate-Water Mesophases by Deuterium NMR and X-Ray Diffraction

Abstract Deuterium NMR and X-ray diffractometry studies of the lyomesophases of the disodium/cromoglycate-water system are reported. The deuterium NMR studies were made on three specifically labelled compounds, viz. disodium cromoglycate-6,8,6′,8′-d4, disodium cromoglycate-3,3′-d2 and disodium cromoglycate-10-d1. The deuterium spectra of these species consist of doublets caused by the corresponding average quadrupolar interaction in the N and M phases; however, in phase III only the methine deuteron of disodium cromoglycate-10-d1 could be seen. The splittings of the chromone moiety deuterons, 3,6 and 8, are essentially identical over the whole temperature and concentration range of the N and M phases, ranging between 50 and 65 kHz. The methine deuteron splitting in the M phase is similar to that of the chromone deuterons, but is considerably higher (115 to 117 kHz) in phase III. The X-ray diffraction studies were made on a 20 wt% solution as a function of temperature between −15°C and 60°C. Two diffraction bands were observed corresponding to approximately 37 Å and 3.4 Å d-values at room temperature. Distinct changes in the diffraction pattern have been observed in the phase transition regions, Isotropic → N → M → III → solid. The results are consistent with a model in which the N and M phases consist of highly ordered cylindrical micelles of stacked disodium cromoglycate molecules whose chromone planes lie perpendicular to the cylinder axes. The 37 Å and 3.4 Å spacings are identified with respectively the intermicellar and intramicellar stacking distances, and from the NMR results the effective orientational order parameter of the micelles is calculated to be between 0.75 and 1.0 depending on the concentration.

Intermicellar correlation in light scattering from dilute micellar solutions of dimethyloleylamine oxide

Angular dependence of light scattering from micellar solutions of dimethyloleylamine oxide has been measured in water and 10 −4 M NaCl at different micelle concentrations from the critical micelle concentration to 0.15 × 10 −2 g cm −3. The angular dissymmetry is lower than unity and decreases with increasing micelle concentration. The observed angular dependence indicates stronger effect of external interference at higher micelle concentrations. The Zernike-Prins equation has been applied to derive the structure factor of micelles by separating the effect of external interference from that of internal interference and by choosing appropriate and consistent values of molecular weight and radius of gyration of micelles. The micelle size becomes larger by the addition of NaCl, and by an increase in micelle concentration. The micelle is rod-like but sufficiently flexible that it may be regarded as spherically symmetric. The radial distribution is obtained for the center of mass of a micelle, and, furthermore, the pair potential is derived by means of the Percus-Yevick equation or the Hypernetted Chain equation for the theory of simple liquids. The micelle molecular weight ranges from 370,000 to 1,030,000, depending on the condition, and, correspondingly, the radius of gyration changes from 213 to 300 Å. The intermicellar interaction distance is located around 1300–1600 Å.

Structure of Micelles of Colloidal Electrolytes. III. A New Long-Spacing X-Ray Diffraction Band, and the Relations of Other Bands

A newly found x-ray diffraction band, obtained from aqueous solutions of soaps and detergents, gives a Bragg spacing which is independent of concentration and is close to the double-length of the molecule. This is designated as the micelle thickness or M-band. The already known long-spacing band, interpreted here as related to the inter-micellar distance, is designated as the I-band. Its spacing dI increases with decreasing soap concentration. If a hydrocarbon is solubilized in the micelles, these spacings increase by ΔdM and ΔdI. Formerly, ΔdI was supposed to give the mean thickness of the layer of oil dissolved between the ends of the hydrocarbon chains of the soap molecules as a middle layer in the micelle. However, ΔdM seems to be more directly related to this thickness. As measured by dM, the thickness of the micelle remains constant with increasing soap concentration: e.g., the values are 40.8, 41.5, 40.7, 40.2, 39.5, 39.6, 40.2A for potassium myristate at 25°C at the following respective concentrations: 2.3, 4.5, 7.2, 9.8, 12.0, 13.7, and 16.5 percent. The mean ``thickness'' increases from 29.7A for potassium caprylate (C8) to 47.3 for potassium palmitate (C16). By a method explained in the text, the number of molecules in a potassium myristate micelle is calculated as 56 at 9.8 percent by use of the Bragg I-spacing. However, it is probable that a corrected Bragg spacing should be used. A new long-spacing band, designated as an X-band, appears when an I-band is present and oil is solubilized in the micelles. The order of spacing is then dI>dM>dX; e.g., in one case the values are 84>50>27A. The ``cylindrical'' model of the micelle preferred here differs from the lamellar and in some respects from the spherical model. It exhibits the following characteristics: (1) A micelle consists of one double-layer of soap or detergent molecules. These have their polar ends oriented outward toward the water and their non-polar ends inward toward each other. (2) The thickness of the micelle of a pure soap is essentially twice the length of the soap molecule, independent of concentration. (3) Hydrocarbons solubilize inside the micelle between the two layers of soap molecules and thus make he micelle thicker. (4) The area per soap molecule in the micelle remains practically constant, whether or not solubilized hydrocarbons are present. (5) The width or lateral dimension of the micelle and the number of soap molecules per micelle increase with increasing soap concentration and with solubilization of hydrocarbons. (6) From energy considerations the area of contact between the hydrocarbon chains of the detergent molecules and the water must be as small as is compatible with the other conditions imposed upon its structure.

Connection of electro-magnetic rotation with uni-polar induction

We present results on the effects of various hydrophobic drugs and additives on the micellar structure of Pluronic F127 solutions. Small-angle neutron scattering experiments on 5 wt% F127 solutions were used to measure micelle core size (R1), micelle corona size (R2), intermicellar interaction distance (Rint), polydispersity (σ), and aggregation number (Nagg); dynamic light scattering was used to measure critical micelle concentration (CMC); and ultraviolet spectroscopy was used to measure drug solubility and apparent micelle–water partition coefficient (Kmw). The core and corona size were found to generally increase in the presence of the drugs, as did Rint. Both σ and Nagg were found to decrease in the presence of most of the drugs, and the CMC was found to vary considerably with no clear correlation. A design of experiments (DOE) approach was used to analyze the results and build empirical correlations. All of the parameters from the SANS experiments were found to depend strongly on drug solubility, with a weak dependence on Kmw in most cases. The aggregation number, however, was found to depend strongly on both Kmw and solubility. The correlations can be used to roughly predict the structural parameters of F127 micelles for other hydrophobic drugs.